闲着无聊，自己写了个几个string.h里的函数练手

1. strtok   没有考虑执行效率问题，代码质量也比较差，不过基本算是完成了任务

    static bool check( char c, const char *token );

    char *strtok( char *str, const char *token )
    {
        int len;
        static char *cur  = 0;
        static char *next = 0;
        if ( token == 0 )
            return str;

        if ( str == 0 )
        {
            if ( next == 0 )
                return 0;
            cur = next;
            len = xl::strlen( cur );
        }
        else 
        {
            len = xl::strlen( str );
            cur = str;
        }

        for ( int i = 0; i < len; i++ )
        {
            if ( check( cur[i], token ) )
            {
                 cur[i] = '\0';
                 next = &cur[i+1];
                 return cur;
            }
        }
        char * ret = next;
        next = 0;
        cur  = 0;
        return ret;
    }
    static bool check( char c, const char *token )
    {
        int len = xl::strlen( token );
        for ( int i = 0; i < len; i++ )
        {
            if ( c == token[i] )
                return true;
        }
        return false;
    }

 

 

 

2. strncpy，模仿写的，不过感觉代码还有优化的空间，自己没太多的测试

主要是从2个角度进行的优化

(1) 32bit内存边界对齐

(2) 机器字长内容复制

ps. 也许写memcpy函数会更好

 

char * strncpy( char *dest, const char *src , int _len )
    {
        char *ret = dest;

        long n = (sizeof(long) - (long)dest % sizeof(long)) % sizeof(long);             

        long len = _len - n;                                  

        if ( len > 0 ) {
            for ( long i = 0; i < n; i++ ) 
                *dest++ = *src++;
        } else if( len < 0 ){
            for ( long i = 0; i < _len; i++ )
                *dest++ = *src++;
            return ret;
        } 

        while( len >= 4 ) {
            *((long *)dest) = *((long *)src);
            dest += sizeof(long);
            src   += sizeof(long);
            len   -= 4;
        }

        while( len > 0 ) {
            *dest++ = *src++;
            len--;
        }
        return ret;
    }